A device used for calibrating protein gel electrophoresis separations is a liquid protein marker. A liquid protein marker includes at least one protein of known molecular weight marked with a tracking dye and ionic components to provide electrical conductance. The protein migrates out of the mixture under the influence of an electrical field at the same rate as the ions. After gel electrophoresis, the migration pattern of a number of protein samples is compared to the migration pattern of the liquid protein marker to determine size or other characteristics of the protein samples.
A problem with liquid protein markers is that they have to be pipetted into wells of the reservoirs. This pipetting step can be burdensome and adds time to the overall process, especially if a large number of gels are loaded (e.g., loading eight gels simultaneously with 96-well automated loaders). Another problem is that with wide wells such as 7.5 mm wide wells, a large volume of the liquid protein marker solution must be added to provide sufficient sensitivity during electrophoresis of the marker. This can significantly increase the cost of a gel run because of the expense of the marker solution. Also, marker solutions must be kept at such low temperatures that they freeze. Repeated freeze/thaw cycles of the marker solution can cause degradation of proteins. A further problem is that only one marker solution can be added per well because multiple marker solutions would mix, giving confusing results.